1. Field of the Invention
The present invention relates to a system for activating a passenger-protecting device such as a curtain airbag mounted on an automotive vehicle.
2. Description of Related Art
As a device for protecting passengers from a rollover of an automotive vehicle, various devices have been proposed: a curtain airbag that is inflated along a side of a vehicle, a seatbelt with a pretensioner winding the seat belt instantaneously, and a device for repeatedly winding a seat belt by a motor.
An example of conventional passenger-protecting device including a curtain airbag is shown in FIG. 10. The curtain airbag 90 is activated, i.e., inflated by an activating system 51 composed of an angular velocity sensor 61 and a control unit 80 that includes a CPU 80a, a ROM 80b and a RAM 80c. An angular velocity ω, when a vehicle is rolling, is detected by the angular velocity sensor 61. The detected angular velocity ω is fed to means 81 that calculates a rolling angle θ by integrating the detected angular velocity ω. The detected angular velocity ω and the calculated rolling angle θ are fed to means 83 that determines that the vehicle is rolling over if both of the angular velocity ω and the rolling angle θ exceed respective predetermined levels. Means 84 activates, i.e., inflates the curtain airbag 90 when it is determined that the vehicle is rolling over.
The conventional activating system, however, is not able to quickly respond to particular situations under which a vehicle rolls over. For example, when a vehicle skids and hits a curb, the vehicle may roll over very quickly. This type of the rollover is referred to as a trip-over-type rollover. When the trip-over-type rollover occurs, passengers sitting on seats are pushed against a side of the vehicle by inertia. Under this situation, the curtain airbag may not be smoothly inflated along the side of the vehicle. In case where the seat belt with a pretensioner or the device for repeatedly winding a seat belt by a motor is used, the passengers cannot be properly protected from being thrown out of the vehicle or from colliding with structures in the vehicle, because the conventional activating system may not respond quickly enough to the trip-over-type rollover.
Another situation under which a quick response of the activating system is required is a so-called flip-over-type rollover. A rollover of a vehicle that occurs when the vehicle runs onto a sharp slope while driving at a high speed is referred to as the flip-over-type rollover. Since this type of rollover occurs instantaneously as the trip-over-type rollover does, the same problems as in the trip-over-type rollover may arise. Therefore, it is very important to detect the trip-over-type and the flip-over-type rollovers in their early stage and to quickly activate the passenger-protecting device.